1. Field of the Invention
The present invention relates to a control apparatus for an AC generator in a vehicle.
2. Prior Art
FIG. 1 shows the arrangement of a conventional control apparatus for an AC generator in a vehicle, in which reference numeral 1 designates an AC generator to be driven by a car engine; 101, an armature coil; 102, a field coil; 2, a rectifier; 201, a main rectification output terminal; 202, an auxiliary rectification output terminal for exciting the field coil 102 by the output; and 203, a grounding terminal. Reference numeral 3 designates a voltage regulator; 301, 304, 311, 318, and 324, transistors; 305, 310, and 323, Zener diodes; 302, 319, and 328 diodes; 303, 306, 307, 314, 315, 317, 319, 320, 321, 322, and 325, resistors; 308, an initial exciting transistor; 313, an initial excitation driving transistor; 316, a voltage detection circuit connecting/disconnecting transistor; 326 and 327, NPN-type Darlington transistors; 312, an oscillator; 4, a battery to be charged by the output of the rectification output terminal 201; 5, a key switch; and 6, a pilot lamp.
The operation of the control device thus arranged will be described hereunder. When the key switch 5 is turned on, a voltage is applied from the battery 4 to the pilot lamp 6 and the resistors 319 and 320 through the key switch 5 to thereby turn the transistor 318 on. Accordingly, the transistors 316 and 313 are also turned on, the initial exciting transistor 308 is actuated to operate, a current is allowed to flow into the field coil 102 to thereby render the field coil 102 in an initial excition state. At the same time, a voltage is applied from the battery 4 to the resistors 306 and 307 through the transistor 316 so that the voltage is detected.
Further, the transistor 313 is turned on so that base current flows respectively into the transistors 326 and 327 through the resistor 325 to thereby turn the transistors 326 and 327 on. A current flows from the battery 4 through the key switch 5, the pilot lamp 6, the diode 328, and the transistors 326 and 327 to thereby light the pilot lamp 6. At that time, the sum of the forward voltage drop (about 0.7V) of the diode 328 and the saturation voltage (about 1.2V) between a collector of the transistor 326 and an emitter of the transistor 327 becomes about 1.9V, so that the transistor 318 is maintained in the on-state.
However, if the voltage of the AC generator 1 becomes high as the engine rotates more rapidly so that the voltage of the battery 4 rises, the Zener diode 305 is rendered conductive so that the transistor 304 is turned on, the transistor 301 is turned off, and the current is stopped flowing into the field coil 102. Further, at that time, the output at the auxiliary output terminal 202 also becomes high and the Zener diode 323 is rendered conductive so that the transistor 324 is turned on, the Darlington transistors 326 and 327 are turned off, and the pilot lamp 6 is also turned off.
In the conventional apparatus described above, the forward voltage drop of the diode 328 is utilized to keep the transistor 318 in the on-state, that is, to keep the initial exciting transistor 308 and the voltage detection circuit connecting/disconnecting transistor 316 in the on-state. Accordingly, the configuration is complicated and expensive.